The photoisomerization of the diarylethylenes

Fluorescence, fluorescence-excitation, and ultraviolet absorption spectra of trans-1-(2-naphthyl)-2-phenylethene conformers

“…* and NPEfl (Scheme 1), that are analogous to s-cis-and j-r/wti-polyene structures, respectively, since the C1C2 bond in naphthalenes is somewhat shorter than the C2C3 bond.291-32-33 Though the possible involvement of NPE,* and NPEfl excited states was considered by Hammond et al in the first study of NPE photoisomerization,34 and Xexc-dependent photoisomerization quantum yields were also reported by Fischer and co-workers,35 it was Kovalenko et al who first concluded that they reflected different photoisomerization efficiencies of the two conformers. 36 The difference in fluorescence behavior of the two conformers was first described by Scheck and Alfimov et al 28•37 and more quantitatively, employing biexponential fluorescence decay analysis, by Haas and the Fischers. 38 The application of kinetic fluorescence analysis (KFA) to the determination of pure component fluorescence and absorption spectra of NPE,* and NPEfl in «-hexane solution at 20 °C was introduced by Birks et Steady-state fluorescence spectra of NPE obtained in MCH for different , and oxygen concentrations also served as the first spectral input matrix for the application of the PCA-SM method to the resolution of pure conformer fluorescence spectra.5 A comparative general description and evaluation of the KFA and PCA-SM methods has been given in a recent review.27 The present work allows a quantitative comparison of these complementary approaches to the resolution of the fluorescence, fluorescenceexcitation, and absorption spectra of NPE* and NPEfl.…”